Conventionally, an overlock machine has been developed that is provided with a plurality of sewing needles for sewing processed fabric and is equipped with a threader that can easily carry out a troublesome operation of threading the needle eyes of a plurality of sewing needles. For example, Patent Document 1 discloses a threader that has a needle bar supported in an oblique direction with respect to the cloth feeding direction in such a manner as to be capable of moving vertically and that carries out threading by catching a thread stretched near the needle eye of a sewing needle attached to the needle bar by a threading hook and allowing the threading hook, which has caught the thread, to move so as to be drawn into the needle eye of the sewing needle.
In overlock machines provided with a plurality of sewing needles, the heights of the needle eyes of the respective sewing needles are different from each other. In the threader disclosed in Patent Document 1, the threading shaft is attached in such a manner as to incline with respect to the direction of vertical motion of the needle bar with the sewing needles attached thereto, the threading shaft is rotated to move the threading hook so that the threading hook approaches or separates from the needle eyes of the sewing needles, and the threading hook, which has caught the thread, can pass through the needle eye of each sewing needle.